1. Field of the Invention
The present invention relates to an electrophotographic photoconductor comprising an electroconductive substrate, and a photoconductive layer formed on the substrate, which has sufficient hardness and mechanical strength, and high photosensitivity and durability.
2. Discussion of Background
Recently, organic photoconductors (OPC) are widely used in copying machines and printers. Such organic photoconductors comprise an electroconductive substrate and a photoconductive layer. The photoconductive layer may comprise a charge generation layer (CGL) and a charge transport layer (CTL) which are successively overlaid on the substrate. The CTL of the conventional photoconductor is in the form of a film which comprises a low-molecular-weight charge transporting material (CTM) which is dispersed in a binder resin in a certain concentration. The addition of the charge transporting material to the binder resin causes deterioration of the mechanical strength of the binder resin itself, and therefore, the CTL is fragile and has a low tensile strength. It is considered that the above-mentioned deterioration of the mechanical strength of the binder resin in the CTL causes some problems of the photoconductor, such as wear, flaw, peeling, and crack.
It is proposed to employ a high-molecular-weight material as the charge transporting material in the CTL. For instance, polymers such as polyvinylcarbazole, polyvinyl anthracene and polyvinyl pyrene reported by M. Stolka in J. POLYM. SCI. VOL. 21, 969; and a vinyl polymer of hydrazone described in '89 JAPAN HARD COPY p. 67 are proposed to use as charge transporting materials in the CTL. However, a film of the CTL is still fragile, and sufficient mechanical strength cannot be obtained. In addition, the above-mentioned high-molecular-weight materials have shortcomings in the sensitivity and the mobility of hole in practice, which induces high residual potential and decreases the durability of a photoconductor.
To solve the aforementioned problems of the CTL, it is proposed that the CTL is formed by previously dispersing a charge transporting material in a binder resin and then curing the binder resin containing the charge transporting material. In this proposal, however, the content of the charge transporting material in the binder resin is as high as 30 to 50 wt. %, so that a sufficient curing reaction is not carried out and the charge transporting material easily falls off the binder resin. The problem of wear of the photoconductor has not yet been solved.
Furthermore, it has also been proposed to add to the photoconductive layer a silicon-containing polymer as disclosed in Japanese Laid-Open Patent Applications 61-219049 and 62-205357; a fluorine-containing polymer as disclosed in Japanese Laid-Open Patent Applications 50-23231, 61-116362, 61-204633 and 61-270768; finely-divided particles of silicone resins and fluorine-containing resins as disclosed in Japanese Laid-Open Patent Application 63-65449; and finely-divided particles of melamine resins as disclosed in Japanese Laid-Open Patent Application 60-177349. However, the compatibility of these additives with the charge transporting material and the binder resin is poor, so that the charge transport layer becomes opaque because of phase separation, accordingly, the electrical characteristics of the charge transport layer is impaired.